Japanese Utility Model Registration No. 3089140 (U.S. Patent Application Publication No. 2003/0123988) discloses in FIGS. 1 to 3 an impeller of an axial flow fan in which a projecting edge 322 curved to form an included angle θ on the upper surface of a blade 32 is formed at a radially outer end portion thereof.
Japanese Utility Model Registration No. 3089140 (U.S. Patent Application Publication No. 2003/0123988) describes that vortices 23 are generated at the radially end portion 13 of the blade as shown in FIG. 5 of the publication if the projecting edge 322 is not formed. Further, the publication describes that the vortex 23 leads to a reduction of static pressure, reduction of air volume, and increase of noise. Furthermore, the publication describes that the formation of the projecting edge 322 allows the static pressure to be increased, air volume to be increased, and noise to be reduced, as compared to when the projection edge 322 is not formed. The inventor of the present invention has confirmed that the effects described in the publication may be obtained. However, from the practical point of view, the amount of dropping at the inflection point appearing in static pressure-air volume characteristics cannot be reduced with a conventional configuration.